As is well know, all piston engines produce some crankcase gases that must be emitted from the crankcase. These crankcase emissions, sometimes referred to as “blow-by” gases, are the result of exhaust gases that leak down into the crankcase from the combustion chamber of the engine's piston cylinders via gaps between the cylinder walls and the piston rings due to the high pressures in the cylinders during compression and combustion. Moreover, the volume of these gases increases over time, as the cylinder liners and piston rings wear, thereby producing more exhaust gas leakage from the combustion chambers.
Because of this leakage, the pressure in the crankcase will rise. However, this pressure should ideally be maintained at a level equal to, or slightly less than, atmospheric pressure in order to avoid causing external oil leakage through various gasketed joints. Therefore, in order to prevent the crankcase gases from pressurizing the crankcase, they must be continually vented therefrom.
Though these gases could be vented to the atmosphere, environmental awareness of crankcase emissions has increased significantly in recent years. As engine emissions have been reduced, the crankcase emissions, which contribute to air pollution, have increasingly become a more significant portion of total engine emissions. Recent regulations have eliminated exceptions for crankcase emissions, treating them the same as other exhaust emissions. Therefore, while it is possible to filter and vent the crankcase emissions to the atmosphere, this method can only be employed when the emission requirements can be satisfied for both the exhaust and crankcase emissions combined.
An alternative to venting these gases to the atmosphere is routing them to the air intake, such as, for example, the systems disclosed in U.S. Pat. No. 6,261,333 to Dickson and U.S. Pat. No. 6,575,022 to Schneider et al. However, as these gases pass through the crankcase, they become contaminated with oil mist. If a crankcase vent is connected directly to the air induction system, the dirty, oily mist may have various ill effects on the engine. This is particularly true in turbocharged engines, where the undesirable consequences of unfiltered crankcase emissions introduced into the engine's air intake can include a decrease in the efficiency of the turbocharger due to coke deposits on the turbine, or a reduction in the performance of the intercooler due to the accumulation of oil, and a significant shortening of the life of the engine. Therefore, it is necessary to filter the crankcase gases prior to introducing them into the air induction system of the engine in order to remove oil and soot, thereby requiring the use of additional filtering assemblies, such as an oil mist separator.
Another alternative, therefore, is to route the crankcase emissions to the exhaust system, which typically already includes a mechanism for disposing of undesirable substances in engine emissions. For example, in a diesel powered vehicle, a diesel particulate filter (DPF) may be positioned in the flow path of the exhaust in order to reduce the amount of soot and harmful gases ultimately emitted. A DPF generally comprises a ceramic filter that traps the particulates in the exhaust gas as it flows through the filter. At high exhaust temperatures, these trapped particulates are burned, resulting in harmless carbon dioxide emissions. Typically, the DPF will employ catalysts—via either a separate catalyst section preceding the filter section or a catalyzed wall filter section—to facilitate oxidation, thereby converting harmful compounds—like hydrocarbons and carbon monoxide—into harmless compounds. Similarly, the use of a catalyst can facilitate oxidation of the carbons trapped in the particulate filter to burn these particulates at lower temperatures. However, the use of such a system may require additional energy consumption to pump the crankcase emissions into the exhaust flow.
What is desired, therefore, is a system for venting blow-by gases from the crankcase of an engine. What is further desired is system of crankcase ventilation that does not require additional filtering assemblies to burn harmful compounds in these emissions. What is also desired is a system that does not require excessive energy consumption to vent and filter the gases.